1. Field of the Invention
The present invention relates generally to material handling, and specifically relates to a method and apparatus for isolating and removing a single ply of pliable material such as cloth from a stack of plies and providing the removed ply to a work station for further processing.
2. Description of the Prior Art
In the garment manufacturing industry, pieces of cloth or other pliable material which have been cut according to a pattern are frequently stacked together by material handling equipment for interim storage or transport prior to sewing the material or performing further processing operations. There accordingly arose a need to isolate and remove a single ply from the stack so that the material can be fed into the subsequent processing equipment. Historically, when manual labor was used for many of the tasks in garment manufacture, the equipment operator would manually remove the plies of material from the stack one at a time.
With the introduction of automated high-speed garment manufacturing equipment, there arose a need to provide the supply of material to the equipment rapidly and in an aligned fashion so that the ply of material does not skew during operations such as sewing. Difficulties have been encountered in prior art material handling apparatus in that it has proven difficult to isolate and separate a single ply of material from a stack of material due the tendency of pliable material such as cloth to adhere because of static electricity, frictional clinging, and thread entanglement. The problem is compounded when the single ply is drawn laterally from the stack because the movement of the topmost ply across the stack generates additional static electricity and tends to pull any clinging plies along with the topmost ply, causing misalignment and misregistration of the plies beneath what was the topmost ply.
Various methods have been proposed for isolating and removing a single ply. In one approach, a vacuum head including a plurality of serrated teeth or needles contacts the topmost ply and lifts a portion of the ply. The sharp teeth frictionally engage the ply so as to assist in the removal of the ply since the vacuum alone may not be generally sufficient to hold a ply of porous material such as cloth as the ply is removed from the stack.
One problem with this device is that the teeth sometimes actually punch through the material and prick the next ply in the stack, thereby tending to pull more than one ply from the stack. Accordingly, a fine adjustment of the depth of needle penetration is required to insure that only the top ply is penetrated, thereby creating difficulties in compensatng for different types and thicknesses of material.
In an attempt to overcome the difficulty with this approach, a second vacuum head has been proposed to attempt to hold the second ply in the stack as the first ply is removed. This creates additional complexity in insuring that the second vacuum head is placed adjacent the second ply, since a portion of the first ply would actually have to be successfully removed from the stack so that the second vacuum head can be positioned over the next ply in the stack.
A similar approach is employed in U.S. Pat. No. 4,153,240 to Gouley, wherein brushes are used to pull the topmost ply from the stack over a suction block which holds any clinging plies while an adhesive gripping finger above the suction head engages the topmost ply and removes it. The same problem as in the above-mentioned device is encountered in that there is no assurance that the topmost ply has been positively separated from any clinging plies so as to prevent the adhesive gripping finger from carrying more than one ply to the work table. The Gouley device relies upon turning the ply over to attempt to unstick it from the next lowest ply in the stack to lower the risk of removal of more than one element in the stack.
It is known in the art to use various forms of adhesive pick-up devices in order to grasp individual sheets from a stack. Representative of these devices are U.S. Pat. Nos. 3,670,674 to Conner, Jr.; 2,919,129 to Sjostrom; 3,539,177 to Schwenk, et al.; 3,785,638 to Beazley; and 3,386,396 to Jacobs et al. Certain other known devices employ rollers to attempt to remove excess sheets or plies from a sheet being transported. Representative of these devices are U.S. Pat. Nos. 3,773,317 to Kummerer; 3,937,453 to Hickey et al.; 3,944,211 to Rasmussen et al.; and 4,208,046 to Shimizu. While these latter devices have proven effective in handling flat, sheet-like materials such as paper and the like, they have not been as successful in handling limp materials such as cloth because of the characteristic of cloth to cling because of friction and static electricity. These roller-type devices appear to depend upon the presence of a degree of longitudinal stiffness in the plies being removed so that the lower plies may be pushed away as the topmost plies are being removed.
Certain other known devices use air jets to separate additional plies from the topmost ply. Representative of this approach are U.S. Pat. Nos. 3,670,674 to Conner, Jr. and 3,539,177 to Schwenk et al.
After a single ply is isolated, there still remains the problem of registering or aligning the removed ply so that it may be fed into a work station such a sewing machine. U.S. Pat. No. 3,386,396 to Jacobs et al. shows a combined automatic sewing machine assembly having a feeder foot which includes indexed adhesive tape for picking up a ply, and which uses air jets to position the work piece for folding. U.S. Pat. Nos. 3,588,096 to Laiter et al. and 3,531,107 to Rovin et al. align the fabric pieces with pulsating jets of air. U.S. Pat. No. 3,411,772 to Roven attempts to register a workpiece with suction devices.
The problem with these and other similar registration devices is that the stops typically used to register the piece of fabric have vertical surfaces which the peripheral edges of the plies have a tendency to climb. This can cause warping, misregistration and buckling due to the limpness of the plies if the plies are continued to be forced toward the stop after the peripheral edge has touched the stop.